Unit 1: Challenges for society
What do Scientists do?
You need to know…
• How the predictive power of science is
based on induction and how scientists
work by proposing and testing hypotheses.
• How competing theories are judged by
their success at prediction, and if several
explanations are equally possible, the
simplest is favoured (Occam’s Razor)
Why should you care?
• You’ve all studied ‘How Science Works’ in
Science GCSEs – you should know loads
already!
• Anyone studying a Science at AS will
continue to study ‘How Science Works’.
• Your understanding of any subject you
study will be enriched if you can analyse
its methods and any ‘scientific’ claims.
A very brief history of ‘scientific method’
• Aristotle’s natural philosophy last for many
hundreds of years – he deduced many
theorems about the natural world from
observation. Didn’t really do any
experiments though; creating ‘artificial
situations’ was no longer studying nature.
Whilst the church taught Aristotle's theories in
the middle ages, Ibn al-Haytham (Alhazen,
Basra, 965–1039) was one of the first key
figures in developing a ‘scientific method’ more
recognisable to us now, the emphasis being on
seeking truth through experiments.
Francis Bacon published ‘Novum Organum’ in
1620. In it he called for natural philosophy to be
based on inductive reasoning from observations.
• Scientists weren’t even called ‘scientists’
until 1833, when William Whewell gave that
name to ‘a systematically-working natural
philosopher’.
• History of the Inductive Sciences (1837) and
The Philosophy of the Inductive Sciences,
Founded Upon Their History (1840).
• “Invention, sagacity, genius are required at
every step in scientific method. It is not
enough to base scientific method on
experience alone; multiple steps are needed
in scientific method, ranging from our
experience to our imagination, back and
forth”.
• Many more attempts have been made since
then to pin down what the ‘scientific method’
is and why (or if) it produces such great
theories.
What do scientists do?
• Make models about the natural world:
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Design experiments
Design equipment
Calibrate equipment
Measure phenomena
Record anomalies
Calculate acceptable ‘error’
Explain or ignore anomalies
Come up with new theories
The Scientific Method
Prior knowledge
Observations
Possible explanations
(hypotheses)
Assess and select
hypothesis
No
?
Yes
Results consistent
with explanation?
Make a prediction
Design + carry out
experiments
The Scientific Method
• Something we do ‘naturally’?
• Where is the induction?
• Where is the deduction?
• Any room for creativity?
Semmelweis
• A Hungarian physician working
in a free maternity hospital in
Vienna in the 1840s.
• The hospital had two clinics; the
‘first clinic’ and the ‘second
clinic’.
• Deaths from puerperal fever were much
higher in the first clinic than the second.
• Semmelweis observed the higher death rate in the
first clinic, and the fact that doctors in the first
clinic also had dissection duties.
• His close friend, another doctor, had recently died
due to blood poisoning after cutting himself during
a dissection.
• He formed the hypothesis that some unobserved
pathogenic agent was being carried on the
doctor’s hands from dissection to treating women
giving birth.
• In 1847 he tested the hypothesis by insisting
doctors to wash their hands in chlorinated lime
after dissection.
• Death rates from puerperal fever in the first clinic
quickly dropped to that of the second clinic.
• Semmelweis’ hypothesis was incorporated into the
germ theory of disease after further experiments
published by Louis Pasteur in 1865.
Hindsight is a wonderful thing…
It’s easy to see now that Semmelweis
was right and his critics were
wrong. The challenge of a historian
of Science is to explain why
alternative ideas were so
compelling.
What stopped Semmelweis’ theory from being accepted at
the time?
• Couldn’t observe the ‘pathogen’.
• Class implications of doctors being seen as ‘unclean.
• Resistance to idea of a universal theory of disease
causation.
Criticising the classic model
In ‘the structure of Scientific revolutions’,
published in 1962, Thomas Kuhn argued that
the classic model of Scientific method is a
retrospective ideal, not an accurate
representation of what Scientists actually do.
• How do we come to accept anomalies?
• When do anomalies demand a new ‘paradigm’
(a ‘Scientific revolution’)?
• How does a new paradigm become accepted?
Karl Popper
In the ‘Logic of Scientific discovery’ published in 1934
Popper outlined the problem with induction:
• An inductive statement can never be proved true by
observations; it can only be conclusively falsified.
The green swan example
• Science should be based around trying to falsify
hypotheses, rather than confirm them.
Popper’s demarcation:
• A scientific hypothesis must predict falsifiable
observations.
• An unfalsifiable theory is not scientific.
Popper’s pet peeves
• Psychoanalysis
• Marxism
• Evolution by natural selection.
• What would Popper have made of
‘intelligent design’?
How else do we choose between
theories?
• Theories which predict more observable
phenomena are superior.
• Occam’s razor:
William of Occam was a 14th century scholar who
is credited with the principle that the best
explanation of any phenomenon uses the fewest
assumptions, so is simpler.
‘All other things being equal, simplest is best’.
Simple explanations are also more amenable to
falsification.
The Copernican revolution
• Throughout the middle ages the
Church taught the geocentric model
of the universe.
• The Egyptian-Roman Ptolomy created a
complex model of planetary epicycles to
reconcile the observed retrograde motion
with Aristotle’s assertion that all heavenly
bodies moved in perfect spheres, with the
Earth at the centre.
• It made fairly accurate predictions but it was
very complex and as technology developed it
threw up more and more anomalies.
1543 – Copernicus proposed the
Heliocentric model of the solar system,
contradicting Ptolemy’s Geocentric system.
It was accepted as a predictive model, as it
was simpler and more accurate than
Geocentric models. It took longer for it to
be accepted as a true representation of the
cosmos.